In order to find the level of leukemic cells during remission a differential count of 5,000 leukocytes was made in 91 acute nonlymphocytic leukemia cases during their first complete remission. Patients were divided into three groups according to the level of leukemic cells, i.e., 0-1/5,000, 2-4/5,000 and 5-/5,000. A close correlation was observed between the survival of patients and the level of leukemic cells and their tendency to decrease or increase during remission. All patients in whom leukemic cells rose from 0-1/5,000 to a level higher than 8/5,000 suffered a documented relapse after 4-8 weeks. This method appears to be a good supportive examination for acute leukemia patients during remission.